Have you ever gone to bed for a good night’s rest only to close your eyes and suddenly jerk awake because you feel as if you're falling into the void? These rather unpleasant feelings can disrupt sleep. What happens in our body and mind at that precise moment? How can this phenomenon be explained? Let’s take a closer look...

This phenomenon known as “hypnic jerk” physically results in an increase in muscle activity that varies in intensity based on the individual. Dr. Carl Bazil, director of the Sleep Disorders Center at Colombia University in New York, explains: “One of the things that happens as you fall asleep is your muscles relax, but the awake part may still be stimulating enough that it will temporarily overreact and you get this jerk of muscle activity.”

The subject has been studied relatively little by the scientific community, and experts admit that, for the moment, they do not know the exact causes of the phenomenon. It seems however that it comes from a "neurological battle" in our brains: one part tells us to stay awake while the other encourages us to fall asleep.

While the causes of the phenomenon have not been clearly identified, certain factors appear to trigger hypnic jerks, particularly caffeine, tobacco, and stimulant consumption, as well as a lack of sleep. According to Carl Bazil, caffeine is the most common trigger, particularly when consumed in the evening.

This reflex may be linked to an evolutionary protective reflex in our primate ancestors who fell asleep in trees: “If you’re in a position where your head starts to drop or your limbs start to drop, that may trigger this sort of response back into wakefulness,” said Bazil. He concluded, humorously: It would be kind of a normal process, but also, I guess, theoretically protective to keep people from falling asleep in the tree — or in the meeting, that might not be a good thing either.”